linux-kernel - Re: [PATCH][RFC] dirty balancing for cgroups

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Message-Id: <20080711161349.c5831081.kamezawa.hiroyu@jp.fujitsu.com>
Date:	Fri, 11 Jul 2008 16:13:49 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	yamamoto@...inux.co.jp (YAMAMOTO Takashi)
Cc:	a.p.zijlstra@...llo.nl, linux-mm@...ck.org, menage@...gle.com,
	containers@...ts.linux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH][RFC] dirty balancing for cgroups

On Fri, 11 Jul 2008 14:59:26 +0900 (JST)
yamamoto@...inux.co.jp (YAMAMOTO Takashi) wrote:

> > > >  - This looks simple but, could you merge this into memory resource controller ?
> > > 
> > > why?
> > > 
> > 3 points.
> >  1. Is this useful if used alone ?
> 
> it can be.  why not?
> 
> >  2. memcg requires this kind of feature, basically.
> > 
> >  3. I wonder I need more work to make this work well under memcg.
> 
> i'm not sure if i understand these points.  can you explain a bit?
> 
In my understanding, dirty_ratio is for helping memory (reclaim) subsystem.

See comments in fs/page-writeback.c:: determin_dirtyable_memory()
==
/*
 * Work out the current dirty-memory clamping and background writeout
 * thresholds.
 *
 * The main aim here is to lower them aggressively if there is a lot of mapped
 * memory around.  To avoid stressing page reclaim with lots of unreclaimable
 * pages.  It is better to clamp down on writers than to start swapping, and
 * performing lots of scanning.
 *
 * We only allow 1/2 of the currently-unmapped memory to be dirtied.
 *
 * We don't permit the clamping level to fall below 5% - that is getting rather
 * excessive.
 *
 * We make sure that the background writeout level is below the adjusted
 * clamping level.
==

"To avoid stressing page reclaim with lots of unreclaimable pages"

Then, I think memcg should support this for helping relcaim under memcg.

> my patch penalizes heavy-writer cgroups as task_dirty_limit does
> for heavy-writer tasks.  i don't think that it's necessary to be
> tied to the memory subsystem because i merely want to group writers.
> 
Hmm, maybe what I need is different from this ;)
Does not seem to be a help for memory reclaim under memcg.

Thanks,
-Kame

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